Our objectives are to understand and define the relative importance of key processes in intermediary metabolism in the dveloping rat by biochemical experimentation in vivo. D(-)-3-hydroxybutyrate and acetoacetate have been shown to be important metabolites for respiration and lipid synthesis in the neonate during the myelination period. The experiments described in this project seek to establish the relative importance of the ketone bodies, 3-hydroxybutyrate and acetoacetate, and carbohydrate (glucose) for respiration and for lipid synthesis in the developing rat. To facilitate the study, neonatal rats are to be artificially reared from about four days after birth until 23 days of age by the infusion of the diet (rat milk substitutes) through a miniaturized intragastric cannula. In addition to investigating the conditions under which the artificially reared rat serves as a metabolically uniform and stable preparation for developmental studies, it will be possible to use the intragastric cannula to deliver rat milk substitutes of varied formulation, nutritionally adverse milk diets, abnormal metabolites, and labeled substrates. We propose to study the impact of metabolic perturbations on the utilization of glucose, lactate, and the ketone bodies and delineate favorable and/or unfavorable interrelationships in the metabolism of these substrates during development.